Optical fiber connectors are an essential part of substantially any optical fiber communication system. For instance, such connectors may be used to join segments of fiber into longer lengths; to connect fiber to active devices such as radiation sources, detectors and repeaters; or to connect fiber to passive devices such as switches and attenuators. The central function of an optical fiber connector is the maintenance of two optical fiber ends such that the core of one of the fibers is axially aligned with the core of the other fiber; and consequently, all of the light from one fiber is coupled to the other fiber. This is a particularly challenging task because the light-carrying region (core) of an optical fiber is quite small. In singlemode optical fibers the core diameter is about 8 microns where 1 micron=1 .mu.m=10.sup.-3 mm. Another function of the optical fiber connector is to provide mechanical stability and protection to the junction in its working environment. Achieving low insertion loss in coupling two fibers is generally a function of the alignment of the fiber ends, the width of the gap between the ends, and the optical surface condition of either or both ends. Stability and junction protection is generally a function of connector design (e.g., minimization of the different thermal expansion and mechanical movement effects). An optical fiber connector typically includes a small cylinder with a glass or plastic fiber installed along its central axis. This cylinder is interchangeably referred to as a ferrule or a plug.
In a connection between a pair of optical fibers, a pair of ferrules are butted together--end to end--and light travels from one to the other along their common central axis. In this conventional optical connection, it is highly desirable for the cores of the glass fibers to be precisely aligned in order to minimize the loss of light (insertion loss) caused by the connection; but as one might expect, it is presently impossible to make perfect connections. Manufacturing tolerances may approach "zero," but practical considerations such as cost, and the fact that slight misalignment is tolerable, suggest that perfection in such matters may be unnecessary.
One popular design of an optical fiber connector is shown in U.S. Pat. No. 4,793,683; and its basic components comprise a precision molded plastic conical plug having an optical fiber centered therein, a compression spring disposed about a cylindrical portion of the plug, and a retention collar surrounding the plug and spring. The collar includes external threads that enable it to couple with another connector via a fixture having a precision molded alignment sleeve whose shape is best described as "biconic." This design has been superseded by the connector shown in U.S. Pat. No. 4,934,785 which comprises a cylindrical plug, a base member that holds the plug, a compression spring, and a cap that surrounds the plug and spring. In this design, only the cylindrical plug needs to be of high precision and is typically made from a ceramic material. When joining two of these plugs together, an alignment sleeve is used which comprises a split, thin-walled cylinder made of metal, ceramic or even plastic material. This alignment sleeve need not be as precise as the above-described biconic alignment sleeve.
And while the above connectors perform satisfactorily, further improvements are desirable. For example, because of the growing acceptance of optical fiber as the transmission media of choice for television, data, and telephone (multimedia) communications, the need to provide higher density interconnection arrangements has emerged. All of the above-mentioned simplex optical connectors are constructed in such a way that the ability to stack a large number of them together is limited by the need to manually grasp both sides during insertion and removal from a receptacle or coupling device. Known duplex optical connectors, such as the one shown in U.S. Pat. No. 4,787,706, also require manual access to the opposite sides of its housing during removal from the receptacle or coupling device which precludes high density optical fiber interconnection arrays. Furthermore, it is always desirable to reduce cost while still providing a connector that is immediately acceptable to customers. With these latter desires in mind, reference is made to the art of electrical connectors where, perhaps, the most used and accepted connectors are the ones known as RJ11-type plugs/jacks that are typically used in corded telephone products. These connectors have achieved widespread acceptance because they are inexpensive, they operate reliably, and their operation is readily understood by customers. However, because of the high precision and low insertion loss requirements associated with optical interconnections (particularly between singlemode fibers), RJ11-type designs have been unacceptable for optical connectors. Examples of such electrical connectors are shown in U.S. Pat. Nos. 3,761,869 and 3,954,320.
Recognizing the engineering challenge posed by the alignment of two very small optical fiber cores, it is still desirable to provide connectors which are smaller, less expensive, and yet more convenient for customers to manipulate. Such connectors would be of great commercial importance.